Iceland Volcanic eruption - global impact?

Hundreds of metres under one of Iceland's largest glaciers there are signs of a looming volcanic eruption that could be one of the most powerful the country has seen in almost a century.
Mighty Katla, with its 10km (6.2 mile) crater, has the potential to cause catastrophic flooding as it melts the frozen surface of its caldera and sends billions of gallons of water surging through Iceland's east coast and into the Atlantic Ocean.
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